The present invention relates to reinforcing members, such as cable bolts of the kind used, for example, in underground mines and construction projects to support the walls and roofs of underground excavations and openings. The invention also relates to similar reinforcing members such as pre-tensioned cables and other reinforcements for use in reinforced concrete and other structures.
In coal mines, the cable bolt is normally fixed at the inner end of a hole drilled in the mine roof by means of a two part quick curing resin such as a suitable polyester or epoxy resin. The epoxy resin is inserted into the hole in separate packaged parts and pushed to the end of the hole by insertion of the cable bolt which also causes destruction of the packaging and mixing of the parts. Rotation of the bolt during full insertion ensures proper mixing of the resin which quickly cures to secure the top of the cable bolt in the hole. In some circumstances cement grouting is then pumped into the hole to secure the bolt along its entire length, to the sides of the hole. This method of installation is not limited to coal and other mines.
The above form of cable bolt is generally tensioned (against a face plate) by hydraulic means or by torquing (rotating a nut on a thread attached to the end of the cable bolt). In some cases a cementitious slurry (referred to as cement grout) is then pumped into the hole.
Many different forms of cable bolt have been proposed in the past and the present invention is concerned with the general kind where a number of outer wires are wound around a central core in the form of a straight wire called a king wire. The outer wires are helically wound around the king wire and in some instances the king wire is replaced with a tube which allows the cement grouting to be pumped into the hole from the top down. The central tube can alternatively be used to allow air to escape from the borehole as cement grout is pumped in from the bottom. Cable bolts of the aforementioned general kind are traditionally formed of uniform diameter wire and the king wire is of a slightly larger diameter than the outer wires. The need for the slightly larger diameter king wire is because when the cable bolt is placed under tension the outer wires (usually six in number) compress against each other and cannot compress the king wire which as a consequence could be withdrawn. Therefore in order to distribute load evenly to all wires, including the king wire, it traditionally needs to be of a slightly larger diameter.
As will be appreciated the need to provide one wire of the cable bolt of different diameter causes an inconvenience for the manufacturer who needs to carry an extra stock item which must be readily identifiable and distinguishable from the other wires.
Accordingly it is an object of this invention to provide a reinforcing member such as a cable bolt which reduces the need for a significantly larger diameter king wire in a multi-wire configuration and provides other advantages over existing cable bolts and reinforcements.
The invention provides a reinforcing member formed from a multiplicity of helically stranded wires, at least some of the outermost of said wires of said multiplicity having spaced helical ribs or grooves on their surfaces.
In a preferred form of the invention, at least three of the outermost wires are formed with spaced helical ribs or grooves on their surfaces. Preferably all of the outermost wires are ribbed or grooved. The wires are preferably manufactured from high tensile steel (with a minimum tensile strength of 1570 mPa), the inner wires may be of the same or a different grade of steel, or of other materials (fibreglass, Kevlar and the like). The outer wires may alternatively be helically wound around a circular steel tube.
By forming at least some of the outermost wires with helical ribs or grooves on their surfaces, the need for a significantly larger core or king wire is avoided due to the better keying achieved by the use of ribs or grooves.
In one preferred form of the invention, the reinforcing member, which may be in the form of a cable bolt, is formed from seven wires, comprising a core or king wire, and six outer wires helically wound around said king wire, and at least three of said outer wires, and preferably all, being formed with helical ribs or grooves. The nominal diameter of the wires will generally be between about 4 mm and 9 mm or the diameter of the wire D1 will generally be between 3.8 mm and 8.8 mm. The ribs preferably have a ribbing about 5 to 30% of the nominal diameter and more preferably about 18 to 25% and most preferably 20% of the nominal wire diameter.
Preferably the king or core wire is also formed with helical ribs or grooves and may be of the same diameter as the outer wires, although in accordance with standard practice, may be 2 to 3 per cent larger or even larger if desired, than the outer wires.
The formation of helical ribs or grooves on the king or core wire reduces the likelihood of the core wire xe2x80x9cwalkingxe2x80x9d within the outer helically wound wires and therefore allows the use of a core wire of the same diameter as the outer wires.
The helical ribs or grooves are preferably formed as four start continuous ribs.
In another form the reinforcing member or cable bolt may include a central straight tube and a plurality of said wires helically wound around said tube.